Institute of Multidisciplinary Research for Advanced Materials (IMRAM, Tagen), Tohoku University, 2-1-1, Katahira, Aoba-Ku, Sendai 980-0877, Japan.
J Am Chem Soc. 2013 Jan 16;135(2):651-8. doi: 10.1021/ja303510g. Epub 2012 Dec 31.
We investigated spin states of stable neutral pure-organic radical molecules of 1,3,5-triphenyl-6-oxoverdazyl (TOV) and 1,3,5-triphenyl-6-thioxoverdazly (TTV) adsorbed on an Au(111) surface, which appears as a Kondo resonance because of spin-electron interaction. By using scanning tunneling spectroscopy (STS), a clear Kondo resonance was detected for the TOV molecule. However, no Kondo resonance was detected for TOV molecules with protrusions in the occupied state image and for TTV molecules. Spin-resolved DFT calculations showed that an unpaired π electron was delocalized over the adsorbed TOV molecule, which was the origin of the Kondo resonance. For the TOV molecules with protrusions, we proposed a model in which an additional H atom was attached to the TOV molecule. Calculations showed that, upon transfer of an electron to the verdazyl ring, the unpaired π electron disappeared, accounting for the absence of a Kondo resonance in the STS spectra. The absence of a Kondo resonance for the TTV molecule can be explained in a similar manner. In other words, electron transfer to the verdazyl ring occurs because of Au-S bond formation.
我们研究了吸附在 Au(111)表面上的稳定中性纯有机自由基分子 1,3,5-三苯基-6-氧代-1,2,4,5-四嗪（TOV）和 1,3,5-三苯基-6-硫代-1,2,4,5-四嗪（TTV）的自旋态，由于自旋-电子相互作用，这些分子表现为近藤共振。通过使用扫描隧道光谱学（STS），我们检测到了 TOV 分子的清晰的近藤共振。然而，对于占据态图像中存在突起的 TOV 分子和 TTV 分子，没有检测到近藤共振。自旋分辨的密度泛函理论计算表明，未配对的π电子在吸附的 TOV 分子上离域，这是近藤共振的起源。对于存在突起的 TOV 分子，我们提出了一个模型，即在 TOV 分子上附加一个额外的 H 原子。计算表明，当电子转移到 verdazyl 环时，未配对的π电子消失，这解释了在 STS 光谱中没有近藤共振。TTV 分子没有近藤共振可以用类似的方式解释。换句话说，由于 Au-S 键的形成，电子转移到 verdazyl 环上。
